Aluminium electroplating formulations

ABSTRACT

Electroplating electrolyte compositions including CA.(nAl(C 3 H 7 ) 3 (2-n)AlR 3 ) where n is 0 and less than or equal to 2; C is Li, Na, K, Rb, Cs, NR′ 4 , or mixtures thereof wherein R′ is H, CH 3 , C 2 H 5 , C 3 H 7 , C 4 H 9 , C 5 H 11 , C 6 H 13 , C 7 H 15 , C 8 H 17 , or mixtures thereof; A is H, F, Cl, Br, or mixtures thereof; R is H, halogen, CH 3 , C 2 H 5 , C 3 H 7 , C 4 H 9 , C 5 H 11 , C 6 H 13 , C 7 H 15 , C 8 H 17 , or mixtures thereof; and an aromatic hydrocarbon, aliphatic hydrocarbon, or mixtures thereof are described. Aluminum and magnesium/aluminum electroplating compositions including C.(nAl(C 3 H 7 ) 4 (1−n)AlR 4 ) where n is 0 and less than or equal to 1, where C is a cation such as, li, Na, K, Rb, Cs, or mixtures thereof; R is H or an alkyl such as, CH 3 , C 2 H 5 , C 3 H 7 , C 4 H 9 , C 5 H 11 , C 6 H 13 , C 7 H 15 , C 8 H 17 , or mixtures thereof are also described. The aluminum and magnesium/aluminum electroplating compositions formulation can include a solvent such as, an aromatic hydrocarbon, aliphatic hydrocarbon, or mixtures thereof.

[0001] This application is being filed as a PCT international patentapplication in the name of ALUMIPLATE INCORPORATED, a U.S. corporation,on 30 Apr. 2002, designating all countries except the U.S.

BACKGROUND OF THE INVENTION

[0002] The invention relates generally to the field of electroplatingand more specifically to aluminum and magnesium/aluminum electroplating.

[0003] The science of electroplating has been developed over a number ofyears, beginning perhaps with Ziegler et al., U.S. Pat. No. 2,849,349.This patent is hereby incorporated in its entirety by reference herein.Lehmkuhl et al., U.S. Pat. Nos. 5,007,991 and 5,091,063, and Birkle etal., U.S. Pat. No. 4,417,954 likewise are incorporated in their entiretyby reference herein.

[0004] While electroplating is not a new art, possible advances remain.Areas of possible improvement include, for example, throwing power andcurrent density. Throwing power refers to the ability of anelectroplating solution to deposit metal uniformly on an irregularlyshaped object. Current density refers to the electrical current(amp/dm²) that can be applied across the anode and the cathode duringthe electroplating process.

SUMMARY OF THE INVENTION

[0005] Aluminum electroplating electrolyte compositions includeCA-(nAl(C₃H₇)₃(2-n)AlR₃) where n is greater than 0 and less than orequal to 2; C is Li, Na, K, Rb, Cs, NR′4, or mixtures thereof wherein R′is H, C₁-C₈ alkyl, e.g., CH₃, C₂H₅, C₃H₇, C₄H₉, C₅H₁₁ C₆H₁₃, C₇H₁₅,C₈H₁₇, or mixtures thereof; A is H, F, Cl, Br, or mixtures thereof; R isH, C₁-C₈ alkyl, e.g., CH₃, C₂H₅, C₃H₇, C₄H₉, C₅H₁₁ C₆H₁₃, C₇H₁₅, C₈H₁₇,or mixtures thereof; and an aromatic hydrocarbon, aliphatic hydrocarbon,or mixtures thereof.

[0006] The above aluminum electrolyte composition of theabove-identified formula also includes embodiments where n is from 0 to2 when such aluminum electrolyte compositions are in admixture withother aluminum alkyls, ethers, alkoxy-aluminum alkyls, aluminoxanes, ormixtures thereof.

[0007] Aluminum and magnesium/aluminum electroplating compositionsinclude C(nAl(C₃H₇)₄(1-n)AlR₄) where n is from 0 to 1. C is a cationsuch as, Li, Na, K, Rb, Cs, or mixtures thereof R is H or an alkyl suchas, CH₃, C₂H₅, C₃H₇, C₄H₉, C₅H₁₁, C₆H₁₃, C₇H₁₅, C₈H₁₇, or mixturesthereof. The aluminum magnesium/aluminum electroplating compositionsformulation can include a solvent such as, an aromatic hydrocarbon,aliphatic hydrocarbon, or mixtures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a flow diagram of an electroplating process.

[0009]FIG. 2 is a flow diagram of a pre-treatment process shown as box100 in FIG. 1.

[0010]FIG. 3 is a flow diagram of the pre-treatment process shown inFIG. 2 where a plasma etch is used.

[0011]FIG. 4 is a flow diagram of a blower system for an electroplatingprocess.

[0012]FIG. 5 is a schematic of a bulk plating device for anelectroplating process.

DETAILED DESCRIPTION

[0013] The term “about” is presumed to modify all numeric values,whether or not explicitly indicated. The term “about” generally refersto a range of numbers that one of skill in the art would considerequivalent to the recited value (i.e., having the same function orresult). In many instances, the term “about” may include numbers thatare rounded to the nearest significant figure.

[0014] The term “M” is molar amount commonly used in chemistry. Theformulation examples and claims report values for concentrations in molper mol salt or mol per mol cation.

[0015]FIG. 1 is a flow diagram of an electroplating process. A basemetal enters the electroplating process 10 at a pre-treatment step 100.The base metal can be any material that can be plated with aluminum,magnesium, aluminum/magnesium or the like. The pre-treatment stepprepares the base metal for plating by removing any non-base metalimpurities from the base metal. The pre-treated base metal proceeds to aplating process 120. The plating process 120 plates the base metal withaluminum, magnesium, aluminum/magnesium or the like. The plated basemetal proceeds to a post-treatment process 130. The post-treatmentprocess 130 prepares the plated base metal for further process such as,for example, drying, application of conversion coatings, lubrication,sealers and the like. The pre-treatment, plating and post-treatmentprocesses can take place in an inert atmosphere or under vacuum.

[0016] Pre-treatment

[0017] Pre-treatment provides a clean surface on the piece or base metalto be coated. To remove fat, oxides, and other impurities from thesurface, degreasing, etching, and/or descaling operations are carriedout. Each treatment step is followed by one or more rinsing steps andconducted in such a manner as to minimize loss and to recycle valuablematerial.

[0018]FIG. 2 is a flow diagram of a pre-treatment process shown as box100 in FIG. 1. The base metal enters the pre-treatment process 201 atdegreasing 200. Degreasing 200 removes grease and the like from the basemetal. Degreasing solutions can include surfactants or other degreasingmaterials. The degreased base metal proceeds to a water rinse 205. Thewater rinse 205 removes the degreasing solution from the degreased basemetal.

[0019] The rinsed and degreased base metal proceeds to an electrolyticdegreasing 210 to further degrease the base metal. The further degreasedbase metal proceeds to a water rinse 212. The further degreased andrinsed base metal proceeds to an acid etch 215 to remove oxides from thebase metal. The acid may be any acid capable of removing oxides from thebase metal. The acid etched base metal proceeds to a water rinse 220 toremove any remaining acid from the base metal.

[0020] The etched base metal then can be nickel plated 225. The nickelplating thickness can be 2 micrometers. The nickel plated base metal canbe water rinsed 230 and dried 235.

[0021] The dried nickel-plated base metal enters an air lock 240 andvacuum environment. The plated base metal proceeds to an activation bath245. The activation bath 245 can include an aqueous inorganic acid inaliphatic mono- or di- or tri-hydric alcohol. The inorganic acid may behydrofluoric acid and the alcohol can be ethylene glycol, for example.The composition of the activation bath 245 must be compatible with thebase metal.

[0022] The activated base metal proceeds to an intermediate rinse 250.The intermediate rinse 250 includes a material that is soluble with thelater electrolyte solvent. The intermediate rinse 250 can be analiphatic alcohol such as, for example, diethylene glycol monomethylether or a mixture of the electrolyte solvent with an aliphatic alcoholsuch as, for example, toluene and di-ethylene glycol monomethyl ether.

[0023] A first electrolyte solvent rinse 255 removes remainingintermediate rinse material. The first electrolyte solvent rinse 255 caninclude up to 10% of the aliphatic alcohol used in the intermediaterinse as impurity. A second electrolyte solvent rinse 260 furtherremoves intermediate rinse material. The second electrolyte solventrinse 260 can include up to 1% of the aliphatic alcohol used in theintermediate rinse as impurity. A third electrolyte solvent rinse 265further removes intermediate rinse material. The third electrolytesolvent rinse 265 can include up to 0.1% of the aliphatic alcohol usedin the intermediate rinse as impurity.

[0024] The base metal rinsed with the electrolyte solvent can proceed toan electroplating process 270.

[0025] Plasma Etch Pre-Treatment

[0026]FIG. 3 is a flow diagram of the pretreatment process shown in FIG.2 where a plasma etch is used to remove impurities from greasy andheavily oxidized base metal.

[0027] The base metal enters the pre-treatment process 301 at degreasing300. Degreasing 300 removes grease and the like from the base metal.Degreasing solutions can include surfactants or other degreasingmaterials. The degreased base metal proceeds to a water rinse 305. Thewater rinse 305 removes the degreasing solution from the degreased basemetal.

[0028] The rinsed and degreased base metal proceeds to an electrolyticdegreasing 310 to further degrease the base metal. The further degreasedbase metal proceeds to a water rinse 312. The further degreased andrinsed base metal proceeds to an acid etch 315 to remove oxides from thebase metal. The acid may be any acid capable of removing oxides from thebase metal. The acid etched base metal proceeds to a water rinse 320 toremove any remaining acid from the base metal and dried 335.

[0029] The dried acid etched base metal enters an air lock 340 andvacuum environment. In the vacuum environment, the acid etched basemetal can be plasma etched 342 to remove further impurities from thebase metal. The plasma etch 342 is an aprotic robust process capable ofprocessing a wide variety of materials. The plasma etch 342 bombards thebase metal with charged particles. The charged particles strike the basemetal and “knock off” organic and inorganic impurities from the basemetal surface. The plasma etch pre-treatment process 301 could eliminatemultiple steps, and associated chemical, recycling and waste treatmentcosts, from the normal pre-treatment process 201.

[0030] A solvent rinse 365 follows the plasma etch 342 to remove dustfrom the metal surface to be plated. The solvent rinsed base metal canproceed to an electroplating process 370. If the base metal is onlyslightly greasy and slightly oxidized, it is possible to use thepretreatment process 301 shown in FIG. 3. The parts enter withoutaqueous pretreatment immediately the airlock 340 and vacuum environment.After plasma etch 342 the parts can proceed to an electroplating process370 directly or after a rinse in a solvent 365. The plasma etchpretreatment described in FIG. 3 is an aprotic process like theAl-plating and the Mg/Al-plating itself. The whole process with plasmaetch as pretreatment and plating is totally aprotic and this means it is100% safe not to introduce hydrogen embrittlement. This is especiallyimportant for plating high strength steel for flight sensitive parts.

[0031] Electrolyte Formulations

[0032] The electrolyte formulations described herein are useful foraluminum, and magnesium/aluminum electroplating. Several factors impactelectrolyte development, such as, for example, electrolyte cost,technical and safety concerns, and plating performance.

[0033] Cost concerns include, for example, costs of chemicals requiredduring electrolyte lifetime, costs for electrolyte recycling, costs forwaste disposal and the electrolyte lifetime.

[0034] Technical and safety concerns include, for example, low chemicaltoxicity, low chemical pyrophoricity, low vapor pressure of theelectrolyte solvent at plating temperature and minimal crystallizationdisturbance.

[0035] Plating performance concerns include, for example, high throwingpower and covering power, high maximum current density on a part, 100%anodic current efficiency, 100% cathodic current efficiency (forming apure aluminum layer) and forming a porefree, dense aluminum layer withan appealing visual appearance.

[0036] The inventive electrolyte formulations provide improved throwingpower and improved current density. In particular, the electrolyteformulations are useful in electroplating base materials with eitheraluminum or a combination of aluminum and magnesium and the like.

[0037] Processing

[0038] Electroplating may be accomplished with direct current. Directcurrent provides a current density that is limited since as the currentdensity increases the alkali metal (i.e. potassium, etc.) precipitatestogether with aluminum on the base metal, which decreases the life ofthe electrolyte and changes the corrosion resistance of the platinglayer on the base metal.

[0039] Electroplating may be accomplished at least in part by pulsereverse plating. Pulse reverse plating is a method of electroplatingwhere the electroplating current is periodically reversed. Forwardcurrent pulse time can be 30 to 150% of the time required to put onelayer of aluminum atoms onto the base metal. Reverse current pulse timecan be 1.5 to 5% of the time of the forward current pulse time. Peakreverse current can be 50 to 200% of peak forward current. Periodicpulse reverse current can increase the effective current forward(effective current density) if the periodic pulse reverse current isoptimized. If an electrolyte has 1 A/dm² maximum current density withdirect current, an optimized periodic pulse reverse current can have thefollowing properties:

[0040] forward current: reverse current of 50:2 ms/ms

[0041] peak forward current: peak reverse current ratio of 1:1 Theoptimized periodic pulse reverse current produced an optimized effectivecurrent density of 1.2 A/dm². Thus, the optimized periodic pulse reversecurrent produced an effective plating current density 20% greater than adirect current process.

[0042] The optimized periodic pulse reverse plating produces plated basemetal with equal to or better physical properties for micro hardness,purity of plated layer, evenness of the plating (throwing power),roughness and visual appearance than the optimized direct currentplating.

[0043] Aluminum Electroplating Formulations

[0044] The inventive electrolyte formulations can include a solvent, asalt, an aluminum alkyl and optional enhancers or additions. The moleratio of aluminum alkyl to salt may be 2:1.

[0045] Solvent

[0046] The solvent can be any aromatic or aliphatic hydrocarbon such as,for example, benzene, toluene, xylene, meta-xylene, cumene,diphenylmethane, para-isopropyl-methylbenzene, tetralin, ethylbenzene,anisole, dipropylether, diisoproplyether, dibutylether, tetrahydrofuran,and the like.

[0047] Salt for 2:1 Complex

[0048] The salt is formed by a cation and an anion. The cation may be analkali metal, such as, for example, lithium, sodium, potassium,rubidium, caesium and the like or the cation may be a tetrammonium, andthe like. The anion may be a halogen, such as, fluoride, chloride,bromide and the like or the anion may be an straight or branched,substituted or unsubstituted alkyl, such as, for example, methyl, ethyl,propyl, butyl, and the like. The anion may also be a hydride.

[0049] Al-alkyls for 2:1 Complex

[0050] Aluminum alkyls can be illustrated as R¹AlR₂ where R is hydrogen,halogen or a 1-8 carbon straight or branched chain alkyl, such as, forexample, methyl, ethyl, n-propyl, isopropyl, n-butyl, iso-butyl, pentyl,hexyl, heptyl, octyl, and the like and where R¹ is a 1-8 carbon straightor branched chain alkyl, such as, for example, methyl, ethyl, n-propyl,isopropyl, n-butyl, iso-butyl, pentyl, hexyl, heptyl, octyl, and thelike.

[0051] Tri-propyl-aluminum (TPA) has a thermal stability that is higherthan most other aluminum alkyls. The 2:1 TPA complexes have a highsolubility and a high decomposition voltage, which makes TPA a usefulcomponent in electrolytes for aluminum plating. High platingtemperatures, high concentrations and high maximum current densities canbe used with formulations that include TPA.

[0052] TPA formulations can be expressed as:

CA.(nAl(C₃H₇)₃(2-n)AlR₃)

[0053] where n is greater than 0 and less than or equal to 2. C is acation such as, Li, Na, K, Rb, Cs, NR′4, or mixtures thereof where R′ isa C₁-C₈ alkyl, e.g., CH₃, C₂H₅, C₃H₇, C₄H₉, C₅H₁₁, C₆H₁₃, C₇H₁₅, C₈H₁₇,or mixtures thereof. A is an anion such as, H, F, Cl, Br, or mixturesthereof R is H, halogen, or an alkyl such as, CH₃, C₂H₅, C₃H₇, C₄H₉,C₅H₁₁, C₆H₁₃, C₇H₁₅, C₈H₁₇, or mixtures thereof. The TPA formulation caninclude a solvent such as, an aromatic hydrocarbon, aliphatichydrocarbon, or mixtures thereof TPA complex formulations can includesolvent and optionally an addition.

[0054] When n is equal to 0 (no TPA present in complex), the electrolyteincludes the 2:1 complex, a solvent and an addition. Additions aredescribed below.

[0055] Aluminum and Magnesium/Aluminum Electroplating Formulations

[0056] The inventive electrolyte formulations can include a solvent, asalt, an aluminum alkyl and optional enhancers or additions. The moleratio of aluminum alkyl to salt may be 1:1.

[0057] Solvent

[0058] The solvent can be any aromatic or aliphatic hydrocarbon such as,for example, benzene, toluene, xylene, meta-xylene, cumene,diphenylmethane, para-isopropyl-methylbenzene, tetralin, ethylbenzene,anisole, dipropylether, diisoproplyether, dibutylether, tetrahydrofuran,and the like.

[0059] Cation for 1:1 Complex

[0060] The cation may be an alkali metal, such as, for example, lithium,sodium, potassium, rubidium, caesium, magnesium and the like.

[0061] Anion for 1:1 Complex

[0062] The anion may be an aluminum alkyl. Aluminum alkyl anions can beillustrated as AlR⁶ ₄ where R⁶ is hydrogen or a 1-8 carbon straight orbranched chain alkyl, such as, for example, methyl, ethyl, n-propyl,isopropyl, n-butyl, iso-butyl, pentyl, hexyl, heptyl, octyl and thelike.

[0063] Quad-propyl-aluminum (QPA) has a thermal stability that is higherthan most other aluminum alkyls. The 1:1 QPA complexes have a highsolubility and a high decomposition voltage, which makes QPA a usefulcomponent in electrolytes for aluminum and magnesium/aluminum plating.High plating temperatures, high concentrations and high maximum currentdensities can be used with formulations that include QPA.

[0064] QPA formulations can be expressed as:

C¹.(nAl(C₃H₇)₄(1-n)AlR⁷ ₄)

[0065] where n is from 0 to 1. C¹ is a cation such as, Li, Na, K, Rb,Cs, or mixtures thereof. R⁷ is H or an alkyl such as, CH₃, C₂H₅, C₃H₇,C₄H₅, C₅H₉, C₆H₁₁C₇H₁₃, C₈H₁₇, or mixtures thereof. The QPA formulationcan include a solvent such as, an aromatic hydrocarbon, aliphatichydrocarbon, or mixtures thereof. QPA complex formulations can includesolvent and optionally an addition.

[0066] QPA formulations can include the following:

C¹.(AlR⁷ ₄) and

C¹.(AlR⁷ ₃—H—AlR⁷ ₃)

[0067] or mixtures thereof. C¹ is a cation such as, Li, Na, K, Rb, Cs,or mixtures thereof. R⁷ is H, or an alkyl such as, CH₃, C₂H₅, C₃H₇,C₄H₉, C₅H₁₁, C₆H₁₃, C₇H₁₅, C₈H₁₇, or mixtures thereof.

[0068] When magnesium/aluminum formulations are used, these electrolytesplate aluminum/magnesium alloys onto conductive substrates or basemetals using magnesium and aluminum anodes or anodes made out ofmagnesium/aluminum alloy with the same or similar composition as thedesired plating material. Also, these magnesium/aluminum formulationsare used to dummy plate with aluminum/magnesium alloy anodes ormagnesium anodes to reach the concentration of magnesium alkyls in theelectrolyte required for the magnesium/aluminum alloy plating.

[0069] Additions

[0070] Aluminum alkyls can be added to the aluminum andmagnesium/aluminum formulations defined above including embodimentswhere n is 0 in an amount in excess of the 2 moles of aluminum alkyl toone mole of salt forming the 2:1 complex. Adding aluminum alkyls inexcess can enhance the current density physical property of theformulation. Aluminum alkyls can be illustrated as R¹AlR² where R² ishydrogen, halogen, or a 1-8 carbon straight or branched chain alkyl,such as, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl,iso-butyl, pentyl, hexyl, heptyl, octyl, and the like and R¹ is a 1-8carbon straight or branched chain alkyl, such as, for example, methyl,ethyl, n-propyl, isopropyl, n-butyl, iso-butyl, pentyl, hexyl, heptyl,octyl, and the like.

[0071] Ethers may be added to the formulations, as with aluminum alkyls,to improve the throwing power physical property of the formulation. Theether can be aliphatic or aromatic. Aliphatic ether may include straightchain or cyclic ethers, for example, dimethylether, ethylene glycoldiether, dioxane, tetrahydrofuran, and the like. Aromatic ethers caninclude, for example, anisole and the like.

[0072] Aluminum alkyls may react with trace amounts of oxygen and/orwater to form aluminoxanes and/or alkoxy-compounds. These compounds maybe provided in the formulation via electrolyte recycle streams. Thesecompounds can enhance the physical properties of the formulation.Alkoxy-compounds can be illustrated as R⁵ _(p)Al(OR⁵)_(3-p) where p is0, 1 or 2 and R⁵ is a 1-8 carbon straight or branched chain alkyl, suchas, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, iso-butyl,pentyl, hexyl, heptyl, octyl and the like. Alkoxy-aluminum-alkyls mayinclude R₂ ⁵Al—O—(C₂H₄—O—)_(q)—Al—R₂ ⁵ or R₂ ⁵Al—O—(C₂H₄—O—)_(q)-R⁵ orthe like where q is 0, 1, 2, 3, or 4. Aluminoxanes can be illustrated asR⁴ ₂Al—(O—AlR⁴ ₂)_(m)-OAlR⁴ ₂ or (R⁴AlO)_(n) where m is an integer from1-8, n is an integer from 3 to 8, and R⁴ is a 1-8 carbon straight orbranched chain alkyl, such as, for example, methyl, ethyl, n-propyl,isopropyl, n-butyl, iso-butyl, pentyl, hexyl, heptyl, octyl and thelike. The compound of the formula (R⁴AlO)_(n) is a ring structuredcompound; for example, when n is 3 the compound has the structure

[0073] Particular electrolyte formulations can provide significantadvances in current density and throwing power. Some formulations aredirected to enhancing throwing power, while others are directed toimproving current density or solubility of the complex. Someformulations provide an attractive balance between throwing power andcurrent density. Examples 1-4 illustrate useful formulations.

[0074] Electrolyte Recycling

[0075] Several improved electrolyte recycling procedures are outlinedbelow. In the first procedure,

[0076] Take the old/used electrolyte and evaporate a portion of thesolvent. A portion of the alkoxy compounds will evaporate with thesolvent.

[0077] Cool and crystallize part of the mixture and then separate thealumioxane in the solution and complexes such as crystalline KF*2TEA.

[0078] Use of the complex crystals like KF*2TEA along with someimpurities to create new electrolyte. The impurities are important asthey simplify the separation process and can be used as addition to thenew electrolyte charge. Alternatively,

[0079] Take the old electrolyte and completely evaporate the solvent andthe alkoxy compounds.

[0080] Cool and crystallize the mixture.

[0081] Dissolve the aluminoxanes with ether or an aliphate (C₅H₁₂ toC₁₂H₂₆).

[0082] Separate the dissolved aluminoxanes and solid complexes such asKF*2TEA.

[0083] Use the complex like KF*2TEA along with some impurities to createnew electrolyte. The impurities are important as they simplify theseparation process and can be used as addition to increase solubilityand throwing power of the electrolyte.

[0084] Evaporate the remaining ether or the aliphatic solvent on thecrystals.

[0085] Add the solvent for the electrolyte and dissolve the complex.

[0086] Blower System

[0087]FIG. 4 is a flow diagram of a blower system for an electroplatingprocess. The blower system 401 includes a blower 410 for forcing gasthrough the electroplating process 400. The blower 410 provides gas tothe electroplating process 400 via an exhaust conduit 450. The gas exitsthe electroplating process 400 via an exit conduit 460. The gas may passthrough a condenser 420. The condenser 420 removes energy from the gasand condenses liquid that can be removed from the blower system 401 viaa condensate exit conduit 470 or the condensate can be recycled to theprocess 400 via a condensate return conduit 480. The gas may be recycledto the blower 410 via a gas recycle conduit 490.

[0088] The blower system 401 removes volatile electrolyte impuritiessuch as, for example, AlR₂OC₂H₅ where R is previously defined. Theblower system 401 provides electrolyte bath agitation for the platingprocess. The blower system 401 provides cooling to the electroplatingbath to prevent overheating of the electrolyte during plating. Theblower system 401 provides continuous recycling of rinse solvents suchas toluene since the condensate may contain higher concentrations ofrinse solvent versus the used outlet rinse bath solution. The outletrinse bath is the rinse bath used after plating to rinse off electrolytewith the electrolyte solvent from the plated parts.

[0089] Humidity can be added to the blower system 401 at a humidityintake conduit 430. Humidity may be added to the system prior to openingup the system for maintenance. The liquid can be drained from theelectroplating process 400, however pyrophoric material and combustiblesolvent may remain. Humidity forced through the blower system 401 candestroy this pyrophoric material and the solvent can be condensed andremoved from the system 400 before air is admitted into theelectroplating process during maintenance. Thus, the blower system 401can provide an important safety function to the electroplating process400.

[0090] Bulk Plating Device

[0091]FIG. 5 is a schematic of a bulk plating device 500 for anelectroplating process 10 (see FIG. 1). Bulk plating presents uniqueproblems due to the pieces to be plated (bulk) may be many small, largevolume pieces. An aluminum plating process will plate only the surfaceof the base metal (or bulk) near the anode. A high throwing power of theelectrolyte is advantageous for maximizing plating rate of bulk pieces.The bulk must be mixed continuously to achieve even plating. An aluminumplating system for bulk plating should have a high average plating rateand a low abrasion rate while plating large amounts of small parts.

[0092] Sufficient bath agitation results in a minimal diffusion layeraround the cathode, which achieves the maximum local current density,for example of 1.3 A/dm² and hence the maximum local plating rate of0.64 mils per hour. To maximize plating rate, the bulk should be spreadout to provide a large surface for aluminum nucleation. The bulk surfaceto bulk volume ratio should be high. The bulk surface should alsomaintain a uniform distance to the anode, so that the maximum localplating rate can be achieved over the largest possible area of the bulksurface, resulting in the highest average plating rate.

[0093] Bulk should be mixed carefully with the right tumbling techniqueto achieve low abrasion rates. If the parts spread out, only slightagitation is necessary to get evenly plated parts. Greater mixingresults in better distribution of aluminum on the bulk or parts.Abrasion and mixing should be carefully balanced to get the requiredplating uniformity and bath agitation.

[0094] Bulk plating may be chosen over rack plating after considerationof several considerations:

[0095] 1. Vary large amounts of very small parts can be cheaper toprocess with a bulk system due to eliminated racking time.

[0096] 2. It is possible to plate with a bulk system without unplatedcontact areas on the part to be plated.

[0097] 3. Bulk plating provides more uniform plating by rotationalexposure of the part to the anode.

[0098] 4. Holes can be more properly rinsed in the part with bulkplating systems.

[0099] Bulk plating can be accomplished with a shaker type bulk platingdevice 500 shown in FIG. 5. Initially the parts will be fed through theparts entrance 505 into the shaker type bulk plating device 500. Theshaker type bulk plating device 500 includes a container chain 510 forconveying bulk 550 into the shaker entrance 560 and for collecting bulk550 from the shaker exit 570. The container chain 510 can be made of aplurality of containers 511 or other means for transferring bulk 550from the shaker exit 570 to the shaker entrance 560. The direction ofmotion of the container chain 510 is shown with arrow 515.

[0100] During plating operation, the container chain 510 deposits thebulk 550 into the shaker entrance 560 and collects the bulk 550 from theshaker exit 570 for return to the shaker entrance 560. The electrolytelevel 565 may submerse the entire container chain 510 during the platingprocess. After the bulk 550 is plated, the container chain 510operations change so that the container chain collects the bulk 550 fromthe shaker exit 570 and deposits the bulk 550 in the plated parts exit580. Thus, the container chain 510 will not turn over at the shakerentrance 560 as shown in FIG. 5. The electrolyte level 585 may belowered below the container chain 510 after the bulk is plated so that aspray rinse 590 can rinse the plated bulk 550 before the plated bulk 550reaches the plated parts exit 580. The containers 511 are perforated sothe rinse 590 liquid can drain to the containers 511 below the top levelfor increased rinsing as shown in FIG. 5.

[0101] The bulk shaker device 500 includes one or more cathodic contactareas 540 that may be a perforated phenolic sheet. The bulk shakerdevice 500 includes one or more anodes 530. The anodes 530 can beparallel with the cathodic contact areas 540 and may be a sheet. Thecathodic contact areas 540 can be between the anodes 530. Screening 520can be placed around the cathodic contact areas 540 and the anodes 530.The cathodic contact areas 540 and the anodes 530 can be mounted into aframe on wheels that is moving/shaking back and forth with an amplitudeshown with arrow 545. The bulk 550 enters the shaker entrance 560 and“shakes” down the cathodic contact areas 540 that may be a perforatedphenolic sheet; the bulk 550 may move from a first cathodic contact area540 a to a second cathodic contact areas 540 b to a third cathodiccontact areas 540 c and so on to the shaker exit 570. While on thecathodic contact areas 540 the bulk is plated.

[0102] The plating speed of the bulk shaker device 500 may be threetimes higher than conventional barrel plating systems. The plating timecan be 2.25 hours for an average aluminum plate thickness of 0.4 milsfor a specific electrolyte with a maximum current density of 1.3 A/dm².The amount of bulk can be 1000 lbs or more.

EXAMPLES

[0103] Any of the electrolytes described herein are made using knowntechniques. The first step is to mix the dry toluene and dry salt withthe solvent. Stir and slowly add (under inert gas) the aluminum alkyls.These should be added in order of their reaction heat, with the compoundhaving the lowest reaction heat being added first. For example, add theold electrolyte first, then the dialkylaluminum halogenide, then TPA,then TEA and then TMA. Heat the mixture to 100° C. and stir for 5 hoursto finish the reaction. After that, the electrolyte is ready for eitheruse or for storage. Note that if impure compounds are used, it may benecessary to perform some dummy plating prior to production in order toremove any impurities present in the electrolyte.

Example 1

[0104] Table I shows electrolyte formulations (A through L) that providea good balance between throwing power and current density. Theseformulations are useful for rack plating. TABLE 1 Al-plating electrolytewith a good balance between throwing power and maximum current densityvalues for concentrations in mol per mol salt A B C D E F G H I J K LElectrolyte 2:1 Salt for Cation Sodium 0.4 1 1 0.2 1 1 complex 2:1Potassium 1 0.6 0.5 1 0.9 0.8 1 0.6 complex Tetrammonium 0.5 0.1 0.4Anion Fluoride 1 0.6 0.5 1 0.9 0.8 1 0.6 Chloride 0.5 0.1 0.4 Hydride0.4 1 1 0.2 1 1 Aluminum- Tri-methyl-aluminum 0.4 0.4 0.5 0.4 0.5 0.40.4 0.4 0.2 alkyls for Tri-ethyl-aluminum 1.6 1.5 1.5 1 0.7 0.9 2:1Tri-n-propyl-aluminum 1.6 0.4 1.6 1.6 1.6 1.6 1.6 0.6 0.8 1.1 complexTri-iso-butyl-aluminum 0.3 Di-iso-butyl-aluminum-hydride 0.4 SolventToluene 2.8 4.2 4.1 4.9 2.8 4.1 4.1 4.3 5.8 5.5 Xylene 4.5 Tetraline 6Additions Aluminum- Tri-methyl-aluminum alkyls Tri-ethyl-aluminumTri-n-propyl-aluminum 0.1 Tri-iso-butyl-aluminumDi-iso-butyl-aluminum-hydride Ethyl-aluminum-di-chloride EtherEthylene-glycole-di-methyl-ether Di-ethylene-glycole-di-methyl-etherDioxane Anisole Others Aluminoxanes R₂Al—O—(C₂H₅—O—)n CH₃ 0.2 0.2R₂Al—O—(C₂H₅—O—)n AIR₂ 0.2 Di-alkyl-alkoxy-aluminum

Example 2

[0105] Table 2 shows electrolyte formulations (M through T) thatprovides good throwing power. These formulations are useful for barrelor bulk plating. TABLE 2 Al-plating electrolyte with a good throwingpower values for concentrations in mol per mol salt M N O P Q R S TElectrolyte 2:1 Salt for Cation Sodium 0.2 1 1 complex 2:1 Potassium 0.50.8 0.9 1 0.9 0.6 complex Tetrammonium 0.5 0.1 0.1 0.4 Anion Fluoride0.5 0.8 0.9 1 0.9 0.6 Chloride 0.5 0.1 0.1 0.4 Hydride 0.2 1 1 Aluminum-Tri-methyl-aluminum 0.5 0.5 0.4 0.5 0.2 alkyls for Tri-ethyl-aluminum1.5 0.9 1.5 1.5 1 0.7 0.9 2:1 Tri-n-propyl-aluminum 1.1 1.6 0.6 0.8 1.1complex Tri-iso-butyl-aluminum 0.3 Di-iso-butyl-aluminum-hydride 0.4Solvent Toluene 4.2 5.1 5.2 4.9 4.3 5.8 5.5 Xylene 6 Tetraline AdditionsAluminum- Tri-methyl-aluminum alkyls Tri-ethyl-aluminum 0.2Tri-n-propyl-aluminum 0.4 Tri-iso-butyl-aluminumDi-iso-butyl-aluminum-hydride Ethyl-aluminum-di-chloride 0.05 EtherEthylene-glycole-di-methyl-ether 0.2 0.3Di-ethylene-glycole-di-methyl-ether Dioxane 0.1 Anisole 0.4 OthersAluminoxanes R₂Al—O—(C₂H₅—O—)n CH₃ 0.2 0.2 0.2 0.3 R₂Al—O—(C₂H₅—O—)nAIR₂ 0.3 Di-alkyl-alkoxy-aluminum

Example 3

[0106] Table 3 shows electrolyte formulations (U through CC) thatprovides high current density. These formulations provide fast platingvia high current density and are useful for continuous plating and thepurification of aluminum. TABLE 3 Al-plating electrolyte with a highmaximum current density values for concentrations in mol per mol salt UV W X Y Z AA BB CC Electrolyte 2:1 Salt for Cation Sodium 0.2 1 complex2:1 Potassium 1 0.7 0.7 1 0.7 1 1 0.8 complex Tetrammonium 0.3 0.3 0.3Anion Fluoride 1 0.7 0.7 1 0.7 1 1 0.8 Chloride 0.3 0.3 0.3 Hydride 0.21 Aluminum- Tri-methyl-aluminum 0.2 alkyls for Tri-ethyl-aluminum 0.30.3 0.3 0.3 0.3 0.3 0.3 0.8 0.4 2:1 Tri-n-propyl-aluminum 1.5 1.7 1.71.7 1.7 1.7 1.7 1.2 1.6 complex Tri-iso-butyl-aluminumDi-iso-butyl-aluminum-hydride Solvent Toluene 4 3.8 4.1 4.1 4.1 4.5 4.53 3.4 Xylene Tetraline Additions Aluminum- Tri-methyl-aluminum alkylsTri-ethyl-aluminum 0.3 0.5 0.5 0.4 0.4 0.4 0.4 0.2 Tri-n-propyl-aluminum0.3 0.1 0.1 0.3 0.4 Tri-iso-butyl-aluminum 0.1Di-iso-butyl-aluminum-hydride 0.2 Ethyl-aluminum-di-chloride 0.1 EtherEthylene-glycole-di-methyl-ether 0.4 0.2Di-ethylene-glycole-di-methyl-ether 0.5 Dioxane 0.3 Anisole 0.5 OthersAluminoxanes R₂Al—O—(C₂H₅—O—)n CH₃ 0.3 0.35 0.3 R₂Al—O—(C₂H₅—O—)n AIR₂0.25 0.2 Di-alkyl-alkoxy-aluminum

[0107] In these formulations, an excess of aluminum alkyl provideshigher current densities but also provides for a rougher precipitation(Al-layer) and lower throwing power. Anisol or other ethers; alkoxycompounds such as, for example; R₂ ⁵Al—O—(C₂H₄—O—)_(q)—Al—R₂ ⁵ or R₂⁵Al—O—(C₂H₄—O—)_(q)—R⁵ where q and R⁵ is previously defined;aluminoxanes; dialkylaluminum halogenide compounds can be used to combatthese negative effects. These formulations result in a maximum currentdensity that is increased by more than 100% compared with the valuesachieved with a specific electrolyte with a maximum current density of1.3 A/dm².

Example 4

[0108] The next set of formulations describe a magnesium/aluminumelectroplating electrolyte that provides high current density. It hasbeen found that an improved electrolyte can be developed by replacingQEA as the main aluminum alkyl with another aluminum alkyl like QPA,QMA, QiBA or mixtures thereof. Preferred formulations (DD through MM)are provided in Table 4 below. TABLE 4 Al and Mg/Al-plating electrolytevalues for concentrations in mol per mol cation DD EE FF GG HH II JJ KKLL MM Electrolyte Complex Cation Sodium 0.1 0.2 0.09 0.12 0.2 0.2 1 1 11 Potassium 0.9 0.8 0.91 0.88 0.8 0.8 Anion (Al(CH₃)₄)⁻ 0.2 0.1(Al(C₂H₅)₄)⁻ 0.4 0.3 0.4 0.4 0.3 0.2 0.15 0.1 (Al(C₃H₇)₄)⁻ 0.6 0.5 0.50.6 0.5 0.4 0.33 0.18 0.1 0.9 (Al(C₄H₈)₄)⁻ 0.1 0.4 0.13 (AIRH(C₄H₉)₂)⁻0.2 ((CH₃)₃Al—H—Al(CH₃)₃)⁻ 0.1 ((C₂H₅)₃Al—H—Al(C₂H₅)₃)⁻ 0.3 0.2((C₃H₇)₃Al—H—Al(C₃H₇)₃)⁻ 0.67 0.36 0.2 0.9 ((C₄H₉)₃Al—H—Al(C₄H₉)₃)⁻ 0.26((C₄H₉)₃Al—H—AIH(C₄H₉)₂)⁻ Solvent Toluene 5.5 6.5 6 5.3 6.5 5.5 2.8 3Xylene 4.1 Tetraline 5.4 Additions Aluminum- Tri-methyl-aluminum 0.4 0.2alkyls Tri-ethyl-aluminum 0.7 0.6 0.8 0.7 0.6 0.4 0.3 0.2Tri-n-propyl-aluminum 1.4 1 1 1.4 1 0.8 0.67 0.36 0.2 1.8Tri-iso-butyl-aluminum 0.2 0.8 0.26 Di-iso-butyl-aluminum-hydride 0.4Ether Ethylene-glycole-di-methyl-ether Di-ethylene-glycole-di-methyl-0.2 ether Dioxane Anisole Others Aluminoxanes R₂Al—O—(C₂H₅—O—)n CH₃ 0.1R₂Al—O—(C₂H₅—O—)n AIR₂ 0.1 Di-alkyl-alkoxy-aluminum

[0109] These formulations employ TPA, TIBA and/or TMA as the maincompound, rather than TEA. We have found that this results in a higherthrowing power and a higher current density.

We claim:
 1. An electroplating composition comprising:CA.(nAl(C₃H₇)₃(2-n)AlR₃) wherein: n is greater than 0 and less than orequal to 2; C is Li, Na, K, Rb, Cs, NR′₄, or mixtures thereof wherein R′is a C₁-C₈ alkyl or mixtures thereof; A is H, F, Cl, Br, or mixturesthereof; R is H, halogen, a C₁-C₈ alkyl or mixtures thereof; and anaromatic hydrocarbon, aliphatic hydrocarbon, or mixtures thereof.
 2. Thecomposition according to claim 1, wherein C is Na, K, NR′₄, or mixturesthereof.
 3. The composition according to claim 1, wherein A is F.
 4. Thecomposition according to claim 1, wherein A is Cl.
 5. The compositionaccording to claim 3, wherein C is Li, Na, K, Rb, Cs, or mixturesthereof.
 6. The composition according to claim 4, wherein C is NR′₄. 7.The composition according to claim 1, wherein the aromatic hydrocarbonis toluene, xylene, tetraline or mixtures thereof.
 8. The compositionaccording to claim 1, wherein; C is 1 M K; A is 1 M F; n is 1.6; R isCH₃; and the aromatic hydrocarbon is tetralin.
 9. The compositionaccording to claim 1, wherein; C is 0.6 M K and 0.4 Mtetraalkylammonium; A is 0.6 M F and 0.4 M Cl; n is 0.6; R is C₂H₅ anddi-iso-butyl hydride; and the aromatic hydrocarbon is toluene.
 10. Thecomposition according to claim 1, wherein; C is 1 M Na; A is 1 M H; nis1.1; R is C₂H₅; and the aromatic hydrocarbon is toluene.
 11. Anelectroplating composition comprising: (a) CA.(nAl(C₃H₇)₃ (2-n) AlR₃)wherein: n is 0 to 2; C is Li, Na, K, Rb, C₅, NR′₄, or mixtures thereof,in which R′ is C₁-C₈ alkyl, or mixtures thereof; A is H, F, Cl, Br ormixtures thereof; R is H, halogen, C₁-C₈ alkyl, or mixtures thereof; (b)a member selected from: (i) an aluminum alkyl compound of the formulaR¹AlR₂ wherein R is as defined above and R¹ is a C₁-C₈ alkyl group; (ii)an ether; (iii) an alkoxy aluminum compound of the formula R⁵₂Al(OR⁵)_(3-p) where p is 0, 1 or 2 and R⁵ is a C₁-C₈ alkyl; (iv) analkoxy aluminum alkyl compound of the formula R⁵ ₂Al—O—(C₂H₄O)_(q)—AlR⁵₂ or R⁵ ₂ Al—O—(C₂H₄O)_(q)—R₅, where R⁵ is as defined above and q is 1,2, 3 or 4; (v) an aluminoxane compound of the formula R⁴ ₂Al—(O—AlR⁴₂)_(m)—OAlR⁴ ₂ or (R⁴AlO)_(n) where m is an integer from 1-8, n is aninteger from 3-8, and R⁴ is a C₁-C₈ alkyl; (vi) and a mixture thereof;and (c) an aromatic hydrocarbon, aliphatic hydrocarbon or mixturesthereof.
 12. The composition according to claim 11, wherein (b) is anether.
 13. The composition according to claim 12, wherein the ether isdioxane, anisole, ethylene-glycol-di-methyl-ether,di-ethylene-glycol-dimethyl-ether, or mixtures thereof.
 14. Thecomposition according to claim 11, wherein (b) is an aluminum alkyl ofthe formula R¹AlR₂.
 15. The composition according to claim 14, wherein Ris CH₃, C₂H₅, C₃H₇, C₄H₉ or mixtures thereof.
 16. The compositionaccording to claim 15, wherein R is C₃H₇.
 17. The composition accordingto claim 11, wherein (b) is an aluminoxane of the formula R⁴₂Al—(—O—AlR⁴—)m-OAl⁴ ₂ or (R⁴AlO)_(n) wherein m is an integer from 1-8and R⁴ is C₁-C₈ alkyl, and n is an integer from 3 to
 8. 18. Thecomposition according to claim 17, wherein R⁴ is CH₃, C₂H₅, C₃H₇, C₄H₉,or mixtures thereof.
 19. The composition according to claim 11, wherein(b) is an alkoxy aluminum compound of the formula R⁵ _(p)Al(OR⁵)_(3-p)wherein p is 0, 1 or 2 and R⁵ is C₁-C₈ alkyl or mixtures thereof. 20.The composition according to claim 11, wherein (b) is alkoxy aluminumcompound of the formula R⁵ ₂Al—O—(C₂H₄—O)_(q)R₅ or R₂⁵Al—O—(C₂H₄—O)_(q)—Al—R₂ ⁵ where q is 1, 2, 3, or 4, and R⁵ is C₁-C₈alkyl, or mixtures thereof.
 21. The composition according to claim 13,wherein: (a) C is 0.9 M K and 0.1 M tetraalkylammonium; A is 0.9 M F and0.1 M Cl; n is 0; R is CH₃ and C₂H₅; (b) the member isethylene-glycol-di-methylether; and (c) the aromatic hydrocarbon istoluene.
 22. The composition according to claim 11, wherein: (a) C is 1M K; A is 1 M F; n is 1.6; R is CH₃; (b) the member is a mixture of (i)aluminum alkyls, where R and R¹ are C₃H₇ and R¹ is C₂H₅ and R is Cl, and(ii) an ether being ethylene-glycol-di-methylether; and (c) the aromatichydrocarbon is xylene.
 23. The composition according to claim 11,wherein: (a) C is 0.9 M K and 0.1 M tetraalkylammonium; A is 0.9 M F and0.1 M Cl; n is 0; R is CH₃ and C₂H₅; (b) the member is a mixture of (i)an aluminum alkyl where R and R′ are C₂H₅; (ii) the ether is anisole,and (iv) a compound of the formula R⁵ ₂Al—O—(C₂H₅O)_(q)CH₃; and (c) thearomatic hydrocarbon is toluene.
 24. The composition according to claim11, wherein: (a) C is 1 M K; A is 1 M F; n is 1.5; R is CH₃ and C₂H₅;(b) the member is a compound of the formula R⁵ ₂AlO—(C₂H₅O)_(q)—CH₃; and(c) the aromatic hydrocarbon is toluene.
 25. The composition accordingto claim 11, wherein: (a) C is 0.7 M K and 0.3 M tetraalkylammonium; Ais 0.7 M F and 0.3 M Cl; n is 1.7; R is C₂H₅; (b) the member is amixture of (i) aluminum alkyls, where R¹ is C₂H₅ and R is Cl and R¹ andR are C₂H₅, and (ii) an ether being anisole; and (c) the aromatichydrocarbon is toluene.
 26. The composition according to claim 11,wherein: (a) C is 0.7 M K and 0.3 M tetraalkylammonium; A is 0.7 M F and0.3 M Cl; n is 1.7; R is C₂H₅; (b) the member is a mixture of (i)aluminum alkyls, where R and R′ are C₂H₅ and R and R¹ are isobutyl, and(ii) an ether being ethylene-glycol-di-methylether; and (c) the aromatichydrocarbon being toluene.
 27. An electroplating composition comprising:C.(nAl(C₃H₇)₄(1-n)AlR₄) wherein: n is 0 to 1; C is Li, Na, K, Rb, Cs, ormixtures thereof; R is H, a C₁-C₈ alkyl or mixtures thereof; and anaromatic hydrocarbon, aliphatic hydrocarbon, or mixtures thereof. 28.The composition according to claim 27, further comprising: C¹.(AlR⁷ ₄);and C¹.(AlR⁷ ₃—H—AlR⁷ ₃) wherein C¹ is a cation such as, Li, Na, K, Rb,Cs, or mixtures thereof and R⁷ is H, or a C₁-C₈ alkyl, or mixturesthereof.
 29. The composition according to claim 27, wherein the aromatichydrocarbon is toluene, xylene, tetraline or mixtures thereof.
 30. Thecomposition according to claim 27, further comprising: a member selectedfrom: (i) an aluminum alkyl compound of the formula R¹AlR₂ wherein R isas defined above and R¹ is a C₁-C₈ alkyl group; (ii) an ether; (iii) analkoxy aluminum compound of the formula R⁵ _(p)Al(OR⁵)_(3-p) where p is0, 1 or 2 and R⁵ is a C₁-C₈ alkyl; (iv) an alkoxy aluminum alkylcompound of the formula R⁵ ₂Al—O—(C₂H₄O)_(q)—AlR⁵ ₂ or R⁵ ₂Al—O—(C₂H₄O)_(q)—R⁵, where R⁵ is as defined above and q is 1, 2, 3 or 4;(v) an aluminoxane compound of the formula R⁴ ₂Al—(O—AlR⁴ ₂)_(m)—OAlR⁴ ₂or (R⁴AlO)_(n) where m is an integer from 1-8; n is an integer from 3 to8; and R⁴ is a C₁-C₈ alkyl; (vi) and a mixture thereof.
 31. Thecomposition according to claim 30, wherein the member is an ether. 32.The composition according to claim 31, wherein the ether is dioxane,anisole, ethylene-glycol-di-methyl-ether,di-ethylene-glycol-dimethyl-ether, or mixtures thereof.
 33. Thecomposition according to claim 30, wherein the member is an aluminumalkyl of the formula R¹AlR₂.
 34. The composition according to claim 33,wherein R is CH₃, C₂H₅, C₃H₇, C₄H₉ or mixtures thereof.
 35. Thecomposition according to claim 34, wherein R is C₃H₇.
 36. Thecomposition according to claim 30, wherein the member is an aluminoxaneof the formula R⁴ ₂Al—(—O—AlR⁴—)_(m)—OAlR⁴ ₂ or (R⁴AlO)_(n) wherein m isan integer from 1-8; n is an integer from 3 to 8; and R⁴ is C₁-C₈ alkyl.37. The composition according to claim 36, wherein R⁴ is CH₃, C₂H₅,C₃H₇, C₄H₉, or mixtures thereof.
 38. The composition according to claim30, wherein the member is an alkoxy aluminum compound of the formula R⁵_(p)Al(OR⁵)_(3-p) wherein p is 0, 1 or 2 and R⁵ is C₁-C₈ alkyl ormixtures thereof.
 39. The composition according to claim 30, wherein themember is an alkoxy aluminum compound of the formula R⁵₂Al—O—(C₂H₄—O)_(q)R₅ or R₂ ⁵Al—O—(C₂H₄—O)_(q)—Al—R₂ ⁵ where q is 1, 2,3, or 4, and R⁵ is C₁-C₈ alkyl, or mixtures thereof.
 40. The compositionaccording to claim 30, wherein: (a) C is 0.2 M Na and 0.8 M K; n is 0.5;R is CH₃ and C₂H₅; (b) the member is a mixture of (i) aluminum alkylswhere R and R¹ are each CH₃, C₂H₅ and C₃H₇, and (ii) an ether beingdi-ethylene-glycol-di-methylether; and (c) the aromatic hydrocarbon istoluene.
 41. The composition according to claim 30, wherein: (a) C is0.09 M Na and 0.91 M K; n is 0.5; R is C₂H₅ and C₄H₉; (b) the member isa mixture of (i) aluminum alkyls where R and R¹ are each C₂H₅, C₃H₇ andi-C₄-H₉; and (c) the aromatic hydrocarbon is toluene.
 42. Thecomposition according to claim 30, wherein: (a) C is 1 M Na; n is_(0.1;) R is each C₂H₅; C₄H₉; H and C₂H₅; H and C₃H₇; and H and C₄H₉;(b) the member is a mixture of (i) aluminum alkyls where R and R¹ areeach C₂H₅, C₃H₇, and i-C₄H₉; and (c) the aromatic hydrocarbon istetraline.